Is it possible to migrate ArcGIS Hub to ArcGIS Enterprise?

It is not possible as there is no tool to completely migrate an ArcGIS Hub site to ArcGIS Enterprise. Although the site itself cannot be migrated, the contents of the site can be cloned and moved to ArcGIS Enterprise using ArcGIS API for Python. Refer to Portal for ArcGIS: Common strategies for more information and How To: Copy/clone content from one ArcGIS Online organization or Portal for ArcGIS to another for instructions. When the items are copied, rebuild the ArcGIS Hub site by using the migrated content in Portal for ArcGIS.